Carbon nanotube-bridged graphene 3D building blocks for ultrafast compact supercapacitors

The main obstacles to achieving high electrochemical energy density while retaining high power density are the trade-offs of energy versus power and gravimetric versus volumetric density. Optimizing structural parameters is the key to circumvent these trade-offs. We report here the synthesis of carbon nanotube (CNT)-bridged graphene 3D building blocks via the Coulombic interaction between positively charged CNTs grafted by cationic surfactants and negatively charged graphene oxide sheets, followed by KOH activation. The CNTs were intercalated into the nanoporous graphene layers to build pillared 3D structures, which enhance accessible surface area and allow fast ion diffusion. The resulting graphene/CNT films are free-standing and flexible with a high electrical conductivity of 39 400 S m^-1 and a reasonable mass density of 1.06 g cm^-3. The supercapacitors fabricated using these films exhibit an outstanding electrochemical performance in an ionic liquid electrolyte with a maximum energy density of 117.2 Wh L^-1 or 110.6 Wh kg^-1 at a maximum power density of 424 kW L^-1 or 400 kW kg^-1, which is based on thickness or mass of total active material.